1. Field of the Invention
This invention relates to an optical disk medium and an optical disk recording and reproducing apparatus which are capable of recording and reproducing information with a very small light spot.
2. Description of the Related Art
In a recording optical disk, preformat information has been recorded on the optical disk. When data is recorded-onto the optical disk with an optical disk unit, the preformat information is detected and the recording position for the data is determined by reference to the detected information.
Usually, the recording track formed in spiral fashion on the optical disk is divided into physical segments of a specific length. Addresses representing locations are allocated to the individual segments. The addresses are written as preformatted data.
In an optical disk with a CLV configuration where the recording line density is constant, all of the physical segment lengths are the same. When a physical segment is too long, the time required to seek address information in random access increases. Therefore, a length composed of ten to several tens of physical segments in one circumference is selected.
One known preformatting method is to form a prepit at the head of a segment. In this method, however, the prepit part cannot be used as a data area. To overcome this problem, another known method used in a recent recording medium is to record format information in such a manner that the information is superimposed on the data recording track in the form of a wobble signal caused by the wobbling of the groove.
When the format information is recorded using a wobble signal, such modulation as phase inversion or frequency change is performed. In +R, such an approach is used. In DVD-R, a method of forming prepits discretely on a land between grooves to create format information has been used.
As for the data to be recorded, error correction codes are created for the original data and then the original data is further divided into smaller synchronous frames to form recording data. For example, in a DVD (digital versatile disk), an error correction code block (ECC block) is modulated. Synchronous codes are added at specific intervals, thereby forming a plurality of synchronous frames. The synchronous frames are used as recording data.
Patent documents related to optical disks are as follows:
Jpn. Pat. No. 2,633,817 (reference 1):
A Identification information is shared by a land (L) and a groove (G) and deviates from the center of the land and groove. This is related to the present DVD-RAM disk standard.
Jpn. Pat. Appln. KOKAI Publication No. 4-172623 (reference 2), Jpn. Pat. Appln. KOKAI Publication No. 2000-11460 (reference 3): A recording mark is formed at the position of a groove. The land part has a land prepit for an address. This is related to the present DVD-RW disk and DVD-R disk.
Jpn. Pat. Appln. KOKAI Publications No. 11-149644, No. 2001-34952 (references 4 and 5): A method of recording data in an L (land)/G (groove). Address information is recorded by wobble modulation using the Gray code.
In the case of DVDs, 416 synchronous frames constitute the minimum unit in recording data. Generally, since the data recording length is larger than the physical segment length, a recording data string equivalent to one ECC structure is recorded over a plurality of physical segments. At this time, to facilitate a search after the recording, the recording data string equivalent to one ECC structure is designed to be equal to the length of an integer number of physical segments. In addition, the physical segment length is designed to fit into an integer number of synchronous frames. For the length L of the recording data string, the physical segment length A is expressed as L=mA where m is a natural number. For example, in the +R format, m=4 is satisfied and 104 synchronous frames are recorded in one physical segment.
The problems here are that highly correlative data items are arranged at regular intervals in the recording data string and that format modulation sections (for example, address information) are present at regular intervals also in a physical segment. If the regular intervals of one of them are an integral multiple of the regular intervals of the other, the data belonging to a column in the ECC matrix is superimposed on the format modulation section.
The ECC matrix configured two-dimensionally has a high capability of correcting errors occurring at random. However, when errors concentrate in a specific column or row, the reliability of correcting errors decreases as compared with the case where errors take place at random.
In the case of DVDs that secure a recording/reproducing margin to some extent, there is not too serious a problem in practical use. However, in the case of next-generation optical disks with much higher recording density, the present configuration has the problem that the format information has too significant an effect on the deterioration of the recording/reproducing data.
Furthermore, in recent years, optical disks have been required to have much larger capacity. To realize this, a so-called land-groove optical disk has been developed which uses not only grooves made in an optical disk but also a land between grooves as recording tracks. In the case of the land-groove optical disk, however, the problem is how to configure format information (addresses) for the land recording track and format information (addresses) for the groove recording track.